What are the methods in describing or writing a set?

Answer 1

In general, in mathematics, we write sets to indicate a collection of objects or elements.

For instance, we referring to the variable x, we may state {x ∈ ℤ}. That is, x is an element of integers.

We can also state conditions within the set notation. For instance, within a given domain of mathematics, such as discussing convergence of series, we can state

{x ∈ ℝ | the series ∑an converges}. That is, x is an element of real numbers, such that the series converges.